Method of increasing anhydrous magnesium chloride content in air dried magnesium chloride



35 tent of decomposition may be somewhat con- Patented Dec. 22, 1931 UNITED STATES PATENT ol-"rlca EDWIN O. BARSTOW', OF MID LAND, MICHIGAN, ASSIGNOR. TO THE DOW CHEMICAL COM- PANY, OF MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN METHOD OE INCREASING ANHYDROUS MAGNESIUM CHLORIDE MAGNESIUM CHLORIDE Io Drawing.

o lization, usually MgCl 6H O, is readily separated.

In order to dehydrate such a chloride for the production of anhydrous chloride or a product in which the chloride is largely in the anhydrous form, various methods may be followed, an economical method being the drying of the normal hydrated salt,

. M oizeri o -6 the form with four molecules of water,

i. e., MgCl AH O, in a current of hot air such as the products of combustion of fuel under conditions of temperature regulation and control, whereby the water of crystallization is driven oif and removed in the said air current. In such methods of drying decomposition occurs and the resulting product, even when finished at a drying temperature of 800 0., and although substantially free from crystal water, still contains combined hydrogen and oxygen. By varying the rate of drying, temperature of drying, pressure under which drying is conducted and other conditions affecting the partial pressures and temperatures existing in the dryer, the extrolled, but in all cases there will be found in the product so obtained a quantity of combined hydrogen and oxygen in which the ratio of these elements remains constant indicating that the so-dried product is comprised largely of anhydrous MgCl and a basic salt equlvalent to MgOHCl.

' As a matter of fact when. hydrated-magnesium chloride is dried, either in air, wet or dry, or in any inert atmosphere, whether at normal pressure or in vacuum, until all water as such to ether with hydrochloric acid is driven 011', t ere results a product containing magnesium, chlorine, oxygen and Application filed May 14,

00mm 111 Am DRIED 1928. Serial No. 277,801.

hydrogen. A peculiarity of this roduct is thatif the hydrogen content be gured as water (H 0) and the remaining ox gen be figured as magnesium oxide (M the molecular ratio of the latter to the former is constant at unity no matter what the total content of such hydrogen and oxygen may be, it being understood thatsuch total content will vary depending upon the method and rate of drying. This, it is believed, indicates that the product in question is composed of magnesium chloride anydrous and the oxy-chlorideg0 Cl). For want of a better term this product is herein referred to as air dried magnesium chloride or else as magnesium chloride containing basic magnesiumchloride; however, it is not intended thereby to define the prodnot as one having any precise constitutional formula.

The main object of my present im roved process is to increase the content of t e anhydrous chloridein a ma esium chloride product such as that just escribed, and'to the accomplishment of this and related ends, the invention then consists of the steps hereinafter fully described and particularly pointed out in the claims, the followin d&

scription setting forth but several -o the ways which the principle of the invention may be utilized. 7

By way of general description of the process in hand I subject the hereinbefore described air dried or equivalentrmagnesium chloride product toanatmosphere of HCl, preferably substantially dry'HCl, which isabsorbed by the basic salt with the production of MgCl lLO in accordancewith the following reaction it is suflicient to treat the air dried chloride 1 in a closed vessel by introducing thereinto' a I supply of substantially dry'HCl, the temperature for absorption rat 750 "mm. being 100 MgOHCl, water and hydrochloric acid gas.

The heating is continued until no more gaseous products are evolved, when it will be found that the content of anhydrous chloride has been increased and a product obtained similar to the original air dried product, but

containing a correspondingly reduced content of the basic salt. If the content of an-. hydrous salt has been sufficiently raised by the one operation as described above the product may be withdrawn and used as such, but if it be desired to still further increase the anhydrous chloride content the step of treat- -ment with HCI, followed by further heating tosecure a further dehydration, may be repea'ed one or more times as may be necessary to obtain a final product sufficiently high in anhydrous chloride to meet the requirements in hand.

A convenient method of carrying out my process is as fo lows. Into a suitable closed container, which may be a steel ch amber, is charged a quantity of the air dried product containing the basic salt. The temperature must be below 280 C., if working at one atmosphere pressure, and preferably below 200 C., to permit use of HCl at lower partial pressures. HCI gas, preferably dried, will thenbe admitted and will: be absorbed by the basic salt. Whenno more H01 is absorbed,

the supply of HCl is cut off and the charge is then heated to a temperature above 280 (3., either in'situ, or it may be withdrawn and passed. through a kiln or other convenient type of dryer in which it may be heated, preferably in a current of hot air or of hot products of combustion. The MgCl .H O formed inthe absorption step is here decomposed chiefly into anhydrous chloride together with some of the basic salt.

It 'is known that the air dried product herein treated by my process maybe converted entirely to anhydrous MgCl by drying'in a-cu-rrent' of HCl gas at a temperature at which the .water vapor formed by the absorption of the HCl is driven off as water vaporand is carried away in the current of gas. This method of proceeding is, however, attended with considerable expense and inconvenience, chiefly arising from the necessity to provide a large quantity of dry HCl gas, and to make it economical, such gas must havethe water of deyhdration removed from it so that the gas may be reused by recycling through the dryer. The dehydration of such a gas is diflicult and expensive and the heat losses in recycling are heavy. The drying reaction may only be carried to the final end vwater vapor inhibiting the ormation of the strictly anhydrous salt and time is required for diffusion to act in dissipating the water vapor envelope and substituting the HCl en-.

vironment.

I have found that proceeding in accordance with my improved method there may be obtained a final product containing but a ve small ortion, e. equivalent MgHCl. p g

I prefer to use as starting material an air dried product in the form of chips or flakes or other granulated form which may be readily obtained b air drying the flaked MgCl 6H O or. the aked MgCI iI-I O.

The product obtained by my method is for most purposes the substantial equivalent of the more expensive product which may be obtained by dehydration in a current of 1101 gas and I find same suitable, for instance, as a feed to an electrolytic cell employing a fused bath containing MgCL for the production of metallic magnesium.

Other modes of applying the principle of my invention may be employed instead of the one explained, change bein made as regards the steps herein disclose provided those stated in any of the following claims or their equivalents be employed.

I therefore particularly point out and distinctly claim as my invention 1. The method of increasing the anhydrous magnesium chloride content of air dried magnesium chloride which comprises the steps of absorbing HGl in said air dried chlo-' ride while maintaining the pressure thereon at substantially one atmosphere and temperature thereof below 280 C. and then raisin the temperature of the so treated chloridea ove 280 C. to expel water therefrom as vapor.

2'. The method of increasing the anhydrous magnesium chloride content of air dried magnesium chloride containing a basic component which comprises the steps of absorbing HCl in said air dried chloride under atmospheric pressure while maintaining the temperature'thereof below 280 C. and then heating the so treated material at a temperature above 280 C. in a hot/gaseous current of the products of combustion of fuel to expel water vapor.

3. The method of increasing the anhydrous magnesium chloride content of air dried magnesium chloride containing a basic component which comprises the steps of absorbing HCl in said air dried chloride under atmospheric pressure while maintaining the temperature thereof below 280 C. and then heating the so treated material to a temperature of about 280 to 290 C. in a hot gaseous current of the products of combustion of fuel to expel water vapor.

4. The method of preparing anhydrous magnesium chloride which comprises alternately subjecting air-dried particles of magnesium chloride containing a component of basic chloride to the action of hydrochloric acid gas at a temperature below 280 C. and then heating the product so obtained at a temperature above 280 C. until such basic chloride component is converted substantially to the anhydrous chloride.

5. The method of preparing anhydrous magnesium chloride which comprises alternately subjecting air-dried particles of magnesium chloride containing a component of basic chloride to the action of hydrochloric acid gas at a temperature below 280 C. and then heating the product so obtained at a temperature above 280 C. but not greatly exceeding 290 C. until such basic chloride component is converted substantially to the anhydrous chloride.

6. The method of preparing anhydrous magnesium chloride which comprises alternately subjecting air-dried particles of magnesium chloride containing a component of basic chloride in a closed space to the action of hydrochloric acid gas at a temperature below 280 C. and then heating the product so obtained in a hot gaseous current of products of combustion of fuel at a temperature above 280 C. until such basic chloride component is converted substantially to the anhydrous chloride.

7. The method of increasing the anhydrous magnesium chloride content of air-dried ma esium chloride containing a component of i sic chloride which comprises reacting the same with hydrochloric acid gas to convert such basic chloride to MgGl .H O and then heating the product to expel water from such mono-hydrate, thereby formin a further component of anhydrous chlori e in the final product. i

8. The method of increasing the anhydrous magnesium chloride content of air-dried magnesium chloride containing a component of basic chloride which comprises reacting the same with hydrochloricacid gas to convert such basic chloride to MgC1 .H O and then heating the product in a hot aeriform current to expel water from such mono-hyof basic chloride which comprises reacting the same with hydrochloric acid gas to convert such basic chloride to MgCl .H O and then heating the product by contact with hot gases from the combustion of fuel to expel water from such mono-hydrate, thereby forming afurther component of anhydrous chloride in the final product.

Signed by me, this 10th day of May, 1928.

EDWIN O. BARSTOW.

drate, thereby forming a further component of anhydrous chloride in the final product.

9. The method of increasing the anhydrous magnesium chloride content of air-dried magnesiumachloride containing a component 

